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I am building a GPIO module that actually powers the Raspberry Pi. I am working with Pi 3B boards and want to feed power directly to GPIO pins 2/4 (VCC +5V) and pin 6 (GND,) completely bypassing the micro USB port to save materials cost and complexity.

Raspberry Pi 3B GPIO Pin Out

Is this allowed or is GPIO power only 1-way? I really don't want to fry a board finding out the hard way.

Thanks.

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No you can't power via the GPIO, but you can from the +5V rail connected to the expansion header. You should follow the Foundation recommendations in the HAT specification https://github.com/raspberrypi/hats.

PS Pin 6 is Gnd NOT -5V.

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    I think what Milliways means here is that pins 2 and 4 aren't GPIO's, but they are part of the expansion header and you can use them for "back-powering" (search down the github link for that term). However, you bypass fuses and regulation by doing so and people do show up here on occasion lamenting the fact that they thereby trashed a unit. – goldilocks Jun 27 '16 at 23:31
  • "If the board will back-power the Pi we recommend adding the safety diode as per requirement 2. of the basic add-on board requirements." - I purchased a roll of Zener diodes for this very purpose. Maybe a fuse/breaker isn't a bad idea to add as well. I am trying to keep the price per unit under $20 USD but I think without those features my unit may be problematic. My device already provides over-temp protection and some low cost surge protection isn't hard to implement, although the source power is expected to already be "clean" and protected. – spyderdyne Jun 28 '16 at 13:28

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